On Mon, Jan 21, 2013 at 6:25 PM, Daniel P. Berrange <berrange@xxxxxxxxxx> wrote: > On Fri, Jan 18, 2013 at 09:37:37AM +0800, Nick Jones wrote: >> On Wednesday, January 16, 2013 10:11 PM, Jaroslav Reznik wrote: >> >As the Feature was renamed and the content of Feature has been extended >> >as requested by FESCo, re-announcing it to the community for re-review. >> > >> >See https://fedorahosted.org/fesco/ticket/986 >> > >> >= Features/Fix Network Name Resolution = >> >https://fedoraproject.org/wiki/Features/FixNetworkNameResolution >> > >> >* Detailed description >> >Currently the getaddrinfo() function doesn't work as it was desinged. >> >Many of its features are buggy and cannot be used without extensive >> >workarounds. Many software packages are using getaddrinfo() with such >> >workarounds. Many can trigger its failures. And many packages that don't >> >use getaddrinfo() will be ported in the near future. >> > >> >> One feature I would like to see added to future glibc, is a fully >> asynchronous version of getaddrinfo, and also getnameinfo. >> >> Asynchronous for non filesystem fds at least. >> >> The glibc maintainers don't seem to be against this idea and I am >> willing to put time into design and implementation. > > Perhaps I'm misunderstanding what you're after, but doesn't "getaddrinfo_a" > already provide an async version of getaddrinfo ? > > "Asynchronous Hostname Lookup API" > http://www.akkadia.org/drepper/asynchnl.pdf > > That said I don't see the reverse - getnameinfo_a > In the summary of this Fedora feature for fixing name resolution is this snippet: "Fedora could be seen as the leader in linux networking" getaddrinfo is important for Linux systems, and the existing issues with it's implementation are well worth fixing, but when it comes to DNS, getaddrinfo is holding Fedora and Linux back. Even though DNS is not the only source of 'names' that getaddrinfo can return, it is the most important, and in the context of DNS, getaddrinfo will not let Fedora reach the above stated goal. It's not just the lack of support for asynchronous usage, getaddrinfo is a very feature poor resolver: - No support for alternative DNS record types: mx, txt ((ab)used for a lot of things) - No support for DNSSEC - No TCP fallback for that matter, which is essential for the above - Probably lot more, I'm no expert on dns What is needed for networking leadership is: - a feature rich resolver, supporting the above as well as query and response filtering, ala AI_ADDRCONF - an implementation of an IPv6 migration strategy along the lines of Happy Eyeballs - can be used both asynchronously or synchronously - ideally pulls in no dependencies outside libc, except perhaps libidn - ideally the DNS packet parsing routines use only ANSI C - can be used by both C and C++ applications, and is easily bound to other scripting languages, even in the async case - provides reverse lookup - more I can't think of right now but I hope others will add more The question is does this all get added into glibc? 1) Yes: - glibc getaddrinfo gets updated to support this through the addition of new hints flags and return values, or a new function interface is created instead of shoehorning into the old interface, in any case the old getaddrinfo interface will always be callable using traditional, existing semantics and run time linking to existing apps will not be broken - the nss layer gets rewritten to support asynchronous usage (and decent error reporting and additional lookup domains maybe samba?) - perhaps the resulting work gets packaged into a proposed extension to POSIX 2) No: - simply say: forget it, lets do proper DNS outside of libc I say 1) could be possible over the course of a few years but for now, 2) is more realistic. As a quick summary: I would suggest, in addition to addressing the outstanding bugs and issues covered by the Fedora feature, a flag be added to the set of getaddrinfo parameters that instructs it NOT to do DNS lookups, only perform alternative resource lookups supported by nss. This flag would be something like: AI_NODNS This will allow application developers to make use of getaddrinfo for resolving names using non dns sources (hosts file is DNS, so this means ldap and others), then perform internet domain lookups using an alternative DNS library that is standardised in Fedora. Given that in most systems, the nss alternatives are local file based, and given the option of using nsscache, these lookups could be considered reasonably constrained therefore NOT in need of asynchronous implementations. Over time, the alternative DNS library could be considered for inclusion in the core c library, and could replace the DNS lookup aspect of getaddrinfo, at least for A and AAAA lookups, and more if additional query flags are defined for getaddrinfo or if an alternative function interface is defined. In addition, work can be done to make the nss layer asynchronous, or at least constrain it to local file resources and standardise on the use of nsscache. Or use this effort to re implement a switched name service lookup library, including DNS aspect, outside of glibc. -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
